This invention relates to a method for cathodic protection, which is particularly but not exclusively arranged for use with steel reinforced concrete structure, wherein the structure includes an existing portion having part of the steel elements embedded therein and a fresh portion having part of the steel elements embedded therein.
Cathodic protection of steel elements at least partly embedded in a surrounding layer is well known and one method for this purpose is described in PCT Application CA00/00101 filed 2nd Feb. 2000 and published as WO 00/46422 by the present inventor.
In PCT Published Application WO 94/29496 of Aston Material Services Limited is provided a method for cathodically protecting reinforcing members in concrete using a sacrificial anode such as zinc or zinc alloy. In this published application and in the commercially available product arising from the application, there is provided a puck-shaped anode body which has a coupling wire attached thereto. In the commercially available product there are in fact two such wires arranged diametrically opposed on the puck and extending outwardly therefrom as a flexible connection wire for attachment to an exposed steel reinforcement member.
The puck is surrounded by an encapsulating material such as mortar which holds an electrolyte that will sustain the activity of the anode. The mortar is compatible with the concrete so that electrolytic action can occur through the mortar into and through the concrete between the anode and the steel reinforcing member.
The main feature of the published application relates to the incorporation into the mortar of a component which will maintain the pH of the electrolyte in the area surrounding the anode at a high level of the order of 12 to 14.
In use of the device, a series of the anodes is provided with the anodes connected at spaced locations to the reinforcing members. The attachment by the coupling wire is a simple wrapping of the wire around the reinforcing bar. The anodes are placed in locations adjacent to the reinforcing bars and re-covered with concrete to the required amount.
Generally this protection system is used for concrete structures which have been in place for some years sufficient for corrosion to start. In general, areas of damage where restoration is required are excavated to expose the reinforcing bars whereupon the protection devices in the form of the mortar-covered pucks are inserted into the concrete as described above and the concrete refilled.
These devices are beginning to achieve some commercial success and are presently being used in restoration processes. However improvements in operation and ergonomics are required to improve success of this product in the field.
U.S. Pat. No. 6,193,857 (Davison) assigned to Foseco discloses an anode body in the form of a puck coated with a mortar in which the puck is attached by ductile wires to the rebar within an excavation in the concrete.
The present invention relates to such concrete structures where an existing structural portion is repaired or covered with a fresh portion of concrete. Thus in some cases, the fresh portion may be applied to an excavated patch where existing steel is exposed and covered by fresh concrete. In this case additional steel may or may not be applied into the fresh concrete, depending upon whether the existing steel has deteriorated to where it requires to be supplemented and depending upon the engineering requirements for the completed structure. In other cases, the existing structure may be supplemented by an overlay or covering which is applied onto the underlying concrete without the necessity for excavation. In this case, additional steel may be in some cases applied into the overlay so that the existing steel in the existing concrete remains in place and the new steel in the new concrete is added to provide the engineering requirements for the complete structure.
In some cases it is known, both in an original concrete structure as constructed and in any repairs thereto, to apply a coating such as an epoxy to the steel rebar so as to reduce the corrosion of the steel, primarily by reducing the ionic current between the steel and the concrete. However this is counter-productive in the cathodic protection method, in that the intention is to provide an ionic current between the anode and the steel (generated by the galvanic action between the steel and the anode member) which minimizes corrosion of the steel.
In some cases it is known to apply a material of the type known as a corrosion inhibitor to a concrete so as to reduce the corrosion of the steel therein, again by reducing or preventing the ionic current between the steel and the concrete. However this would be entirely counter-productive in the cathodic protection method, in that the intention is to provide an ionic current between the anode and the steel (generated by the galvanic action between the steel and the anode member) which minimizes corrosion of the steel, and the presence of the corrosion inhibitor would interfere with this ability.
It is one object of the present invention, therefore, to provide an improved method of cathodic protection of steel within a covering where the steel is protected by providing an anode material in or in contact with the covering material which provides an ionic current to the steel through the covering material.
According to a first aspect of the invention, therefore, there is provided a method for cathodic protection comprising:
providing steel material;
applying a covering material such that a part of the steel material is at least partly covered by the covering material;
forming a cathodic protection combination by:
providing at least one anode member;
arranging the at least one anode member in connection with the covering material for communication of ions therebetween;
and electrically connecting the at least one anode member so that an electrical potential between the anode member and the steel material causes ions to flow through the covering material tending to inhibit corrosion of the steel material;
and applying into the combination a corrosion inhibiting material.
According to a second aspect of the invention, therefore, there is provided a method for cathodic protection comprising:
providing an existing structure including an existing covering material;
providing steel material;
applying a fresh covering material to the existing structure such that a part of the steel material is at least partly covered by the existing covering material and a part of the steel material is at least partly covered by the fresh covering material;
providing at least one anode member;
arranging the at least one anode member in connection with the fresh covering material for communication of ions therebetween;
electrically connecting the at least one anode member so that an electrical potential between the anode body and the steel material causes ions to flow through the covering material tending to inhibit corrosion of the steel material;
and increasing the flow of ionic current between the anode member and the steel material within the existing covering material to provide increased protection for the steel material in the existing covering material by reducing the flow of ionic current between the anode member and the steel material within the fresh covering material.
The invention is primarily concerned with galvanic systems in which the anode body is formed from a sacrificial material which corrodes relative to the steel material without the provision of impressed current. The invention is beneficial since the generation of sufficient current to adequately protect the reinforcing steel over a long life in such systems is difficult to achieve. However the same principles as set out herein can also be used in impressed current systems.
The invention is applicable primarily but not exclusively to repairs where an existing structure has fresh covering material added.
The invention is applicable both to repairs where some of the existing covering material is excavated to expose the existing steel and the fresh covering material is applied over the exposed steel, to overlays or new structures where the steel within the fresh covering material is wholly new steel and to arrangements which include both a repair or patch and an overlay.
The term xe2x80x9csteel materialxe2x80x9d as used above is intended to refer generally to any steel component or components which are in contact with the covering material in a manner such that corrosion can occur. The term is used to maintain generality as to the number and type of components within the fresh material and/or the existing material. Such components may be wholly or only partly buried within the covering material. The term may relate to steel reinforcing elements or bars within the covering material, to steel elements within the covering material which are structural and to steel elements within the covering material which are non-structural and non-reinforcing but which can corrode. In many cases the steel material is in the form of a plurality of steel elements, generally reinforcing bars, some of which are in the fresh material and some in the existing material. However the term is intended also to cover arrangement wherein a single element such as a beam extends both into the fresh material and the original or existing material.
While the present invention is primarily concerned with concrete as the covering material, it will be appreciated that it is not so limited and other materials which allow the communication of ions to the reinforcing steel can also require to be protected in this manner.
The existing covering material and the fresh covering material are in most cases the same material and in most cases concrete, but it will be appreciated that the fresh material need not be the same as the original material provided both cooperate with the steel in a galvanic action with the anode members and provided there is communication of ions through the interface between the existing and the fresh materials.
In many cases, the anode member or members are wholly buried or embedded within the covering material. However the anode members may be partially embedded or even located on the surface of the fresh concrete provided they are in ionic communication with the steel in the structure.
Preferably the flow of ionic current between the anode member and the steel material within the fresh covering material is reduced by providing a material which interferes with the communication of ionic current through the interface between the fresh covering material and the steel material therein
In one arrangement, the material can be applied onto the at least one steel element within the fresh covering material as a coating thereon.
In an alternative arrangement, the material can be applied into the fresh covering material at the interface with the steel material therein. In this case, the material is preferably applied into the fresh covering material in admixture therewith, but it also may be applied as an admixture with a small portion of the fresh covering material initially applied over the steel or as a material which remains at the interface.
In a further alternative, the material is carried by the anode member when it is embedded in the covering material for diffusion from the anode member into the covering material.
Where the material is applied into or with the covering material, it is preferably of a character which is a corrosion inhibitor.
Such corrosion inhibitors may be selected from the group consisting of aliphatic and aromatic nitrogen compounds and aliphatic and aromatic phosphorous compounds.
Preferably the material is of a character which avoids inhibiting the ability of the anode to generate an ionic current between the anode member and the covering material
Preferably the material is of a character which avoids significantly increasing the resistivity of the concrete as this would reduce the ability of the anode to pass ionic current to the steel material.
This method is particularly advantageous where the anode body is formed at least partly of finely divided materials which are pressed together and where the anode body includes admixed therewith an enhancement material for co-operating with the sacrificial anode material in enhancing the communication of ions between the covering layer and the anode material, which material is bound into the sacrificial anode material of the solid anode body so as to be carried thereby.
The anode member may advantageously comprises an electrically conductive array which is at least partly formed by said anode material.
According to a third aspect of the invention there is provided a method for cathodic protection comprising:
providing an existing structure including an existing covering material;
providing steel material;
applying a fresh covering material to the existing structure such that at least part of the steel material is at least partly covered by the existing covering material and at least part of the steel material is at least partly covered by the fresh covering material;
providing at least one anode member;
arranging the at least one anode member in connection with the fresh covering material for communication of ions therebetween;
electrically connecting the at least one anode member so that an electrical potential between the anode body and the steel material causes ions to flow through the covering material tending to inhibit corrosion of the steel material;
and applying into the fresh covering material at least at the interface with the steel material therein a material of a character which reduces the flow of ionic current between the steel material and the fresh covering material without substantially increasing the resistivity of the fresh covering material and without substantially inhibiting the flow of ionic current between the anode member and the fresh covering material.
The material applied within the fresh covering material thus increases the proportion or ratio of current flowing to the existing steel material. It may or may not decrease the total ionic current due to the reduction of current to the steel material in the fresh covering material. There is, due to the increase in the proportion or ratio, however a net tendency to increase the cathodic protection to the existing steel where it is primarily required.